Comparison of human turning gait with the mechanical performance of lower limb prosthetic transverse rotation adapters.

Given the importance of minimizing transverse plane shear stress on soft tissue, several transverse rotational adapters (TRAs) are available for incorporation in lower limb prostheses. This study compares kinetic and kinematic data from human subjects during straight and turning gaits to the mechanical performance of several TRAs. Physiological data were collected from three individuals walking straight and turning at self-selected speeds around a 1 m radius circle. The average peak torques and range of motion for normal subjects while turning were 8.2 Nm and 26 degrees (outside leg), 11.8Nm and 20 degrees (inside leg), and 11.4 Nm and 20 degrees (right leg) during straight gait. Each TRA was mechanically tested without axial loading in a servo-hydraulic material testing system (MTS) over its rotational range at 0.5 dergrees/s and 60 degrees/s. The TRAs with axial compression were also tested at 0.5 degrees/s under a 736N (75kg mass) axial load. Applying these torques to the different TRAs yielded 3 to 35 degrees rotation, depending on the elastomer installed. Some TRAs had nearly constant stiffness, while others stiffened with rotation. The TRAs also varied in their average maximum stiffness from 0.4Nm/degree to 2.7Nm/degrees. Normal subjects exhibit interior vs. exterior asymmetrical torques and displacements; however, only one of the TRAs is designed to allow asymmetrical stiffness, and none have asymmetric ranges. Prosthetists and physicians can use these data to better interpret amputees' qualitative remarks and to prescribe the correct TRA and/or elastomer. This information also forms a basis for further design and development of novel torque absorbing prosthetic adapters.